Bioassays are widely used for observing changes in a cellular state or response of a cell to a drug or the like. Conventional bioassays often employ culture cells. Since pluralities of cells are used in such a system to carry out an assay, an average value of the cell population is regarded as the property of a single cell.
In reality, however, cell cycles of cells of such a population hardly synchronize with each other, where respective cells express proteins at different cycles. Accordingly, there has always been a problem of fluctuation in analyzing the resulting responses to stimulation.
Specifically, since fluctuations are ubiquitously present in the response resulting from the reaction mechanisms of cells, only average response can be always obtained. In order to solve these problems, techniques such as synchronous culture have been developed. However, constant use of a group of cells at the same stage means to continuously supply such cells, which has been standing in the way of widely promoting bioassays.
In addition, since there are two types of stimulations (signals) given to a cell, i.e., those given depending on the amounts of signal molecules, nourishment and dissolved gas contained in the liquid around the cell, and those given due to physical contact/intercellular interaction with other cells, the situation has been difficult in order to judge the fluctuations.
The problems of physical contact/intercellular interaction between the cells can be solved to a certain degree by conducting a bioassay with a cell mass such as a tissue fraction. In this case, however, unlike culture cells, a cell mass with constant uniformity is not always available. Thus, there are problems of the resulting data being fluctuating or information being unnoticeable in such a population.
In order to measure an information processing model having each of the cells in a cell group as the minimum structural unit, the inventors of the present application have proposed, as described in Japanese Patent Laid-Open Application No. 2006-94703 (Patent document 1), a cell population microarray (bioassay chip) having a plurality of cell culture partitions for confining cells to particular spatial configurations, where adjacent partitions are connected via grooves or tunnels which do not allow cell passage therethrough, and, if necessary, a plurality of electrode patterns are applied to the grooves, tunnels or cell culture partitions for measuring changes in the potentials of the cells.    [Patent document 1] Japanese Patent Laid-Open Application No. 2006-94703